holbrook@alliant.alliant.com (Mark Holbrook) (12/18/90)
I need a device to give me an binary electrical indication that water is flowing/not flowing through a standard half-inch domestic water pipe. I could build one, but surely such a widget must already exist. Any pointers? My local plumbing supply house hasn't a clue. Mark Holbrook Alliant Computer Systems Corporation Phone: (508) 486-1262 1 Monarch Drive FAX: (508) 486-1398 Littleton, MA 01460 E-mail: holbrook@alliant.COM
bill@videovax.tv.tek.com (William K. McFadden) (12/19/90)
In article <4390@alliant.Alliant.COM> holbrook@alliant.alliant.com (Mark Holbrook) writes: >I need a device to give me an binary electrical indication that water >is flowing/not flowing through a standard half-inch domestic water >pipe. This is only a partial solution, but you can detect the turn-on of hot water by the temperature rise on the pipe. You can detect the flow rate with two sensors. This only works at startup, though. -- Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077 bill@videovax.tv.tek.com, {hplabs,uw-beaver,decvax}!tektronix!videovax!bill Phone: (503) 627-6920 "The biggest difference between developing a missle component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI
larry@kitty.UUCP (Larry Lippman) (12/20/90)
In article <6229@videovax.tv.tek.com>, bill@videovax.tv.tek.com (William K. McFadden) writes: > >I need a device to give me an binary electrical indication that water > >is flowing/not flowing through a standard half-inch domestic water > >pipe. > > This is only a partial solution, but you can detect the turn-on of > hot water by the temperature rise on the pipe. You can detect the > flow rate with two sensors. This only works at startup, though. If one penetrates the pipe with a small point-type heating element, and uses two temperature sensors, one slightly downstream of the other, one can measure flow rate based upon the rate of heat transfer determined by the delta-T. This is the priciple behind one type of mass flowmeter, such as manufactured by Hastings. However, this is probably far too complex and expensive for the application presented by the author of the original article. If this were an industrial application where $100 to $150 is not a problem to spend, one of the simplest and least expensive flow sensors utilizes a spring-loaded vane, which when deflected by fluid flow will move a preset distance and operate a microswitch or reed switch. Inexpensive paddle-wheel flow sensors, such as those manufactured by Signet, connected to an indicator with a setpoint may also be used in industrial environment. For a DIY project involving minimum expenditure, I will make two suggestions: 1. Install a pipe fitting such that a slight restriction is created in the pipe diameter. Couple a piezoelectric ultrasonic sensor (often used in alarm motion detectors, and readily available on the surplus market for a few dollars) to the outside of the pipe using a clamp, or possibly epoxy adhesive. Ultrasonic energy will be created during fluid flow by vortices formed at the restriction, with this energy being readily detectable by a suitable ultrasonic sensor (a miniature ceramic microphone with good high frequency response may be a satisfactory substitute for an actual ultrasonic sensor). The ultrasonic energy created should be sufficiently broadband that even ultrasonic sensors with narrow bandpass should work. One of the best restrictions can be created by a sharp annulus or orifice plate inserted within the pipe; one should not restrict the cross-sectional area of the pipe by more than say, 20%. The ultrasonic sensor output is amplified, fed through high-pass filter, rectified and fed to an adjustable comparator. One might also wish to throw in some time delay and hysterisis. Comparator threshhold is set to provide an output when a suitable flow rate is detected. With proper design, this device should be immune to extraneous ultrasonic energy conducted by the pipe from other sources. One could easily begin experimentation with the above approach by merely connecting a microphone or ultrasonic sensor to an amplifier, and observing the output on an oscilloscope. Somewhat more complex variations of the above are used in industry to provide quantitative flow measurement, with the most common example being the vortex-shedding flowmeter. The above design suggestion does not represent a vortex-shedding approach, however. 2. Create an internal orifice plate as above, and install tees with sidearms as small as possible before and after the orifice plate. Differential pressure in the low in-H2O range will be created by flow fluid across the orifice plate. Differential pressure switches that are adjustable may readily be found on the surplus market, with a common original application being aircraft fuel flow sensing. One could also use a surplus differential pressure transducer, but the differential pressure switch would be a much simpler approach. Be careful in using some differential pressure sensors: they may be damaged if inadvertently connected in a non-differential manner (i.e., some devices are unable to withstand water line pressure on one port if the other were open to atmosphere). Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 {utzoo, uunet}!/ \aerion!larry
whos@ddsw1.MCS.COM (Ben Feen) (12/20/90)
Do you wanna know if the water is FLOWING in the pipe, or just SITTING in the pipe? -- whos@ddsw1.MCS.COM | I don't know, who's at DDSW1? | whos@ddsw1.MCS.COM! I asked YOU who's at DDSW1! Ok, there's a guy at DDSW1, right? | Right! Who? | Exactly! | What? | No, he's at lll-winken. | Where? | No, What! | I don't know! | He's at gargoyle. | Who? | No, he's at DDSW1.MCS.COM!
whit@milton.u.washington.edu (John Whitmore) (12/20/90)
In article <4258@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: (original query) >> >I need a device to give me an binary electrical indication that water >> >is flowing/not flowing through a standard half-inch domestic water >> >pipe. > >2. Create an internal orifice plate as above, and install tees with > sidearms as small as possible before and after the orifice plate. > Differential pressure in the low in-H2O range will be created by > flow fluid across the orifice plate. Differential pressure switches > that are adjustable may readily be found and for that matter, differential pressure sensors with bridge outputs can be conditioned for any given flowrate threshold. The main problem with this approach is: it will howl like a banshee if the associated piping is tuned for any audible wavelength (which is rather likely in a domestic installation.) The orifice/pipe combination is a water-powered whistle. You might want to use a loop of smaller-diameter (copper?) pipe instead, so simple laminar flow (with drag on the sidewalls of the pipe) is created. The differential pressure will go as the square of the fluid velocity, roughly. This is the fluid equivalent of a resistive element, and the differential pressure gauge is the equivalent of a voltmeter, so is equivalent to a VOM in current measurement mode. John Whitmore